Macro metric

macro_rules! metric {
    (
        name: $name:expr,
        help: $help:expr
        $(, subsystem: $subsystem_name:expr)?
        $(, const_labels: { $($cl_key:expr => $cl_value:expr ),* })?
        $(, var_labels: [ $($vl_name:expr),* ])?
        $(, buckets: $bk_name:expr)?
        $(,)?
    ) => { ... };
}

Available on crate feature metrics only.

Define a metric for use in materialize.